Noise reduction in reluctance machines

Abstract

In a switched reluctance machine, the air gap between aligned rotor and stator poles is defined to have an inner region of substantially uniform length and outer regions of increasing length. The outer regions are flanked by extension portions on one or both of the poles that form a radiussed transition region on the pole between each outer region and a side wall of the pole. The at least one of the poles has a waist portion between the extension portions and the body of the lamination. As the rotor rotates with respect to the stator, alignment of the poles more gradually modifies the flux path such that radial forces tending to distort the stator and give rise to vibration and acoustic noise are reduced. The waist portion decreases the inductance of the stator winding in the minimum inductance position of the rotor.

What is claimed is: 
     
       1. A set of laminations for a reluctance machine, comprising: a rotor lamination and a stator lamination, each respective lamination having a body and an array of poles extending radially from its respective body about an axis, each pole being substantially symmetrical about a center line and having a pole face and side surfaces extending between the body and the pole face, the pole faces of the rotor poles and the pole faces of the stator poles cooperating to define respective air gaps therebetween when the laminations are arranged on a common axis and the center lines of the rotor poles and the center lines of the stator poles are coincident, each air gap having an inner region of substantially constant radial length and an outer region, on either side of the inner region, of progressively greater radial length extending away from the inner region, one or both of the said rotor poles and stator poles having an extension on the side of each outer region, the extension smoothly merging each outer region with a corresponding side surface, and at least one of the laminations having an undercut defining a waist in said one or both poles between each extension and the body, the pole faces having dimensions adapted to provide a smoothly changing flux path as the rotor pole moves into and out of alignment with the stator pole, thereby tending to reduce vibration and acoustic noise for a given output of the reluctance machine, wherein the inner region extends angularly up to four times an angular width of one of the outer regions. 
     
     
       2. A set as claimed in claim 1 in which both the inner region and the outer regions have an angular extent, further in which each rotor pole face has an arcuate surface over the angular extent of both the inner region and the outer regions, the arc of the arcuate surface coinciding with a diameter centered on the said common axis. 
     
     
       3. A set as claimed in claim 2 in which the extensions are on the stator pole and lie angularly beyond the said arcuate surface of the rotor pole face. 
     
     
       4. A set as claimed in claim 3 in which the waist of the stator pole has a chordal width less than a greatest chordal width between the extensions. 
     
     
       5. A set as claimed in claim 1 in which both the inner region and the outer regions have an angular extent, further in which the stator pole face has an arcuate surface over the angular extent of both the inner region and the outer regions, the arc of the arcuate surface coinciding with a diameter centered on the said common axis. 
     
     
       6. A set as claimed in claim 5 in which the extensions are on the rotor pole and lie angularly beyond the said arcuate surface of the stator pole face. 
     
     
       7. A set as claimed in claim 6 in which the chordal width of the waist of the rotor pole is less than a greatest chordal width between the extension regions. 
     
     
       8. A set as claimed in claim 1 in which the rotor poles and stator poles are shaped such that the air gap in each outer region increases radially to about twice a radial length of the air gap in the inner region. 
     
     
       9. A reluctance machine comprising a stator and a rotor made up of a stack of the set of laminations as claimed in claim 1. 
     
     
       10. A machine as claimed in claim 9, in which the rotor is mounted to rotate within the stator. 
     
     
       11. A set of laminations for a reluctance machine, comprising: a rotor lamination and a stator lamination, each respective lamination having a body and an array of poles extending radially from its respective body about an axis, each pole being substantially symmetrical about a center line and having a pole face and side surfaces extending between the body and the pole face, the pole faces of the rotor poles and the pole faces of the stator poles cooperating to define respective air gaps therebetween when the laminations are arranged on a common axis and the center lines of the rotor poles and the center lines of the stator poles are coincident, each air gap having an inner region of substantially constant radial length and an outer region, on either side of the inner region, of progressively greater radial length extending away from the inner region, one or both of the said rotor poles and stator poles having an extension on the side of each outer region, the extension smoothly merging each outer region with a corresponding side surface, and at least one of the laminations having an undercut defining a waist in said one or both poles between each extension and the body, the pole faces having dimensions adapted to provide a smoothly changing flux pa th as the rotor pole moves into and out of alignment with the stator pole, wherein the inner region extends angularly up to four times the angular width of one of the outer regions. 
     
     
       12. A set as claimed in claim 11 in which both the inner region and the outer regions have an angular extent, further in which each rotor pole face has an arcuate surface over the angular extent of both the inner region and the outer regions, the arc of the arcuate surface coinciding with a diameter centered on the said common axis. 
     
     
       13. A set as claimed in claim 12 in which the extensions are on the stator pole and lie angularly beyond the said arcuate surface of the rotor pole face. 
     
     
       14. A set as claimed in claim 13 in which the waist of the stator pole has a chordal width less than a greatest chordal width between the extensions. 
     
     
       15. A set as claimed in claim 11 in which both the inner region and the outer regions have an angular extent, further in which the stator pole face has an arcuate surface over the angular extent of both the inner region and the outer regions, the arc of the arcuate surface coinciding with a diameter centered on the said common axis. 
     
     
       16. A set as claimed in claim 15 in which the extensions are on the rotor pole and lie angularly beyond the said arcuate surface of the stator pole face. 
     
     
       17. A set as claimed in claim 16 in which the chordal width of the waist of the rotor pole is less than a greatest chordal width between the extension regions. 
     
     
       18. A set as claimed in claim 11 in which the rotor poles and stator poles are shaped such that the air gap in each outer region increases radially to about twice a radial length of the air gap in the inner region. 
     
     
       19. A reluctance machine comprising a stator and a rotor made up of a stack of the set of laminations as claimed in claim 11. 
     
     
       20. A machine as claimed in claim 19, in which the rotor is mounted to rotate within the stator. 
     
     
       21. A set of laminations for a reluctance machine, comprising: a rotor lamination and a stator lamination, each respective lamination having a body and an array of poles extending radially from its respective body about an axis, each pole being substantially symmetrical about a center line and having a pole face and side surfaces extending between the body and the pole face, the pole faces of the rotor poles and the pole faces of the stator poles cooperating to define respective air gaps therebetween when the laminations are arranged on a common axis and the center lines of the rotor poles and the center lines of the stator poles are coincident, each air gap having an inner region of substantially constant radial length and an outer region, on either side of the inner region, of progressively greater radial length extending away from the inner region, one or both of the said rotor poles and stator poles having an extension on the side of each outer region, the extension smoothly merging each outer region with a corresponding side surface, and at least one of the laminations having an undercut defining a waist in said one or both poles between each extension and the body, the pole faces having dimensions adapted to provide a smoothly changing flux path as the rotor pole moves into and out of alignment with the stator pole, wherein the rotor poles and stator poles are shaped such that the air gap in each outer region increases radially to about twice the radial length of the air gap in the inner region. 
     
     
       22. A set as claimed in claim 21 in which both the inner region and the outer regions have an angular extent, further in which each rotor pole face has an arcuate surface over the angular extent of both the inner region and the outer regions, the arc of the arcuate surface coinciding with a diameter centered on the said common axis. 
     
     
       23. A set as claimed in claim 22 in which the extensions are on the stator pole and lie angularly beyond the said arcuate surface of the rotor pole face. 
     
     
       24. A set as claimed in claim 23 in which the waist of the stator pole has a chordal width less than a greatest chordal width between the extensions. 
     
     
       25. A set as claimed in claim 21 in which both the inner region and the outer regions have an angular extent, further in which the stator pole face has an arcuate surface over the angular extent of both the inner region and the outer regions, the arc of the arcuate surface coinciding with a diameter centered on the said common axis. 
     
     
       26. A set as claimed in claim 25 in which the extensions are on the rotor pole and lie angularly beyond the said arcuate surface of the stator pole face. 
     
     
       27. A set as claimed in claim 26 in which the chordal width of the waist of the rotor pole is less than a greatest chordal width between the extension regions. 
     
     
       28. A set as claimed in claim 21 in which the inner region extends angularly up to four times an angular width of one of the outer regions. 
     
     
       29. A reluctance machine comprising a stator and a rotor made up of a stack of the set of laminations as claimed in claim 21. 
     
     
       30. A machine as claimed in claim 29, in which the rotor is mounted to rotate within the stator. 
     
     
       31. A set of laminations for a reluctance machine, comprising: a rotor lamination and a stator lamination, each respective lamination having a body and an array of poles extending radially from its respective body about an axis, each pole being substantially symmetrical about a center line and having a pole face and side surfaces extending between the body and the pole face, the pole faces of the rotor poles and the pole faces of the stator poles cooperating to define respective air gaps therebetween when the laminations are arranged on a common axis and the center lines of the rotor poles and the center lines of the stator poles are coincident, each air gap having an inner region of substantially constant radial length and an outer region, on either side of the inner region, of progressively greater radial length extending away from the inner region, one or both of the said rotor poles and stator poles having an extension on the side of each outer region, the extension smoothly merging each outer region with a corresponding side surface, and at least one of the laminations having an undercut defining a waist in said one or both poles between each extension and the body, the pole faces having dimensions adapted to provide a smoothly changing flux path as the rotor pole moves into and out of alignment with the stator pole, thereby tending to reduce vibration and acoustic noise for a given output of the reluctance machine, wherein the rotor poles and stator poles are shaped such that the air gap in each outer region increases radially to about twice a radial length of the air gap in the inner region. 
     
     
       32. A set as claimed in claim 31 in which both the inner region and the outer regions have an angular extent, further in which each rotor pole face has an arcuate surface over the angular extent of both the inner region and the outer regions, the arc of the arcuate surface coinciding with a diameter centered on the said common axis. 
     
     
       33. A set as claimed in claim 32 in which the extensions are on the stator pole and lie angularly beyond the said arcuate surface of the rotor pole face. 
     
     
       34. A set as claimed in claim 33 in which the waist of the stator pole has a chordal width less than a greatest chordal width between the extensions. 
     
     
       35. A set as claimed in claim 31 in which both the inner region and the outer regions have an angular extent, further in which the stator pole face has an arcuate surface over the angular extent of both the inner region and the outer regions, the arc of the arcuate surface coinciding with a diameter centered on the said common axis. 
     
     
       36. A set as claimed in claim 35 in which the extensions are on the rotor pole and lie angularly beyond the said arcuate surface of the stator pole face. 
     
     
       37. A set as claimed in claim 36 in which the chordal width of the waist of the rotor pole is less than a greatest chordal width between the extension regions. 
     
     
       38. A set as claimed in claim 31 in which the inner region extends angularly up to four times an angular width of one of the outer regions. 
     
     
       39. A reluctance machine comprising a stator and a rotor made up of a stack of the set of laminations as claimed in claim 31. 
     
     
       40. A machine as claimed in claim 39, in which the rotor is mounted to rotate within the stator.